Systems and methods for maximizing signal integrity on circuit boards

Abstract

A circuit board may include a plurality of electrically-conductive layers separated and supported by layers of insulating material laminated together and a via electrically coupled to a first layer of the circuit board and coupled to a second layer of the circuit board, the via comprising a first via portion comprising electrically-conductive material and having a first diameter and a first depth from a surface of the circuit board and a second via portion comprising electrically-conductive material and having a second diameter smaller than the first diameter and a second depth from the first depth.

What is claimed is: 
     
       1. A circuit board, comprising:
 a plurality of electrically-conductive layers separated and supported by layers of insulating material laminated together; 
 a first via having a uniform diameter throughout; and 
 a second via electrically coupled to a first layer of the circuit board and coupled to a second layer of the circuit board, the second via comprising: 
 a first via portion comprising electrically-conductive material and having a first diameter and a first depth from a surface of the circuit board; and
 a second via portion comprising electrically-conductive material and having a second diameter smaller than the first diameter and a second depth from the first depth; wherein both the first diameter and the second diameter of the second via are smaller than the uniform diameter of the first via. 
 
 
     
     
       2. The circuit board of  claim 1 , wherein:
 the first via portion comprises a first cylindrical tube of the first diameter; and 
 the second via portion comprises a second cylindrical tube of the second diameter in series with the first via portion. 
 
     
     
       3. The circuit board of  claim 2 , wherein together the first cylindrical tube and the second cylindrical tube form one continuous tube of differing diameters. 
     
     
       4. The circuit board of  claim 1 , wherein the first diameter and the second diameter are approximately concentric. 
     
     
       5. The circuit board of  claim 1 , wherein the second via comprises a layer of electrically-conductive material formed on interior walls of an opening through the circuit board. 
     
     
       6. The circuit board of  claim 1 , wherein a sum of the first depth and the second depth equals a thickness of the circuit board. 
     
     
       7. An information handling system comprising:
 an enclosure; and 
 a circuit board housed in the enclosure, the circuit board comprising:
 a plurality of electrically-conductive layers separated and supported by layers of insulating material laminated together; 
 a first via having a uniform diameter throughout; and 
 a second via electrically coupled to a first layer of the circuit board and coupled to a second layer of the circuit board, the second via comprising: 
 
 
       a first via portion comprising electrically-conductive material and having a first diameter and a first depth from a surface of the circuit board; and
 a second via portion comprising electrically-conductive material and having a second diameter smaller than the first diameter and a second depth from the first depth; 
 wherein both the first diameter and the second diameter of the second via are smaller than the uniform diameter of the first via. 
 
     
     
       8. The information handling system of  claim 7 , wherein:
 the first via portion comprises a first cylindrical tube of the first diameter; and 
 the second via portion comprises a second cylindrical tube of the second diameter in series with the first via portion. 
 
     
     
       9. The information handling system of  claim 8 , wherein together the first cylindrical tube and the second cylindrical tube form one continuous tube of differing diameters. 
     
     
       10. The information handling system of  claim 7 , wherein the first diameter and the second diameter are approximately concentric. 
     
     
       11. The information handling system of  claim 7 , wherein the second via comprises a layer of electrically-conductive material formed on interior walls of an opening through the circuit board. 
     
     
       12. The information handling system of  claim 7 , wherein a sum of the first depth and the second depth equals a thickness of the circuit board. 
     
     
       13. A method for forming a circuit board, comprising:
 forming a plurality of conductive layers separated and supported by layers of insulating material laminated together; 
 forming a first via between layers of the circuit board; the first via having a uniform diameter throughout; and 
 forming a second via electrically coupled to a first layer of the circuit board and coupled to a second layer of the circuit board, the second via comprising:
 a first via portion comprising electrically-conductive material and having a first diameter and a first depth from a surface of the circuit board; and 
 a second via portion comprising electrically-conductive material and having a second diameter smaller than the first diameter and a second depth from the first depth; 
 wherein both the first diameter and the second diameter of the second via are smaller than a diameter of the first via. 
 
 
     
     
       14. The method of  claim 13 , wherein:
 the first via portion comprises a first cylindrical tube of the first diameter; and 
 the second via portion comprises a second cylindrical tube of the second diameter in series with the first via portion. 
 
     
     
       15. The method of  claim 14 , wherein together the first cylindrical tube and the second cylindrical tube form one continuous tube of differing diameters. 
     
     
       16. The method of  claim 13 , wherein the first diameter and the second diameter are approximately concentric. 
     
     
       17. The method of  claim 13 , wherein the second via comprises a layer of electrically-conductive material formed on interior walls of an opening through the circuit board. 
     
     
       18. The method of  claim 13 , wherein a sum of the first depth and the second depth equals a thickness of the circuit board. 
     
     
       19. The method of  claim 13 , wherein forming the second via comprises:
 forming a first hole with the first diameter from the surface of the circuit board to the first depth; 
 forming a second hole with the second diameter from the first depth; and 
 plating interior surfaces exposed by the hole with electrically-conductive material. 
 
     
     
       20. The method of  claim 13 , wherein:
 forming the first hole comprises drilling the first hole with a first drill bit having approximately the first diameter; and 
 forming the second hole comprises drilling the second hole with a second drill bit having approximately the second diameter.